Waxes, which commonly are derived from natural and synthetic sources, have been incorporated into coating and ink systems for the purpose of altering surface properties such as gloss and water repellency in the resulting ink and coating. Waxes have been incorporated into aqueous coatings and ink formulations generally by four techniques. These technologies include molten wax, emulsification, dispersion, and micronization. The molten wax technique involves melting the wax in hot solvents having a boiling point higher than the melting point of the wax and dispersing the resultant mixture into the resin. Emulsified waxes are incorporated into aqueous systems through the use of dispersants and surface active materials to maintain stability. Dispersed waxes are generally produced by grinding the wax into a solvent and/or vehicle in a ball mill or roll mill. Micronized waxes are prepared by introducing the wax into a high-speed impeller and mixing with other components for forming a coating of ink.
There is a need for water based polymer containing emulsion, containing wax in graphic arts and coating industries. Some of the applications are in low moisture vapor barrier transmission (MVTR) coatings, barrier coatings and non-skid top coatings. The most prevalent method for incorporating waxes has been to disperse the wax into water and then add the aqueous wax dispersion to the emulsion or to the ink and coating formulations.
Emulsions having waxes incorporated by these methods are not without problems. These methods often limit the type and the amount of the wax that can be incorporated into aqueous emulsions and they often require substantial quantities of surfactants which can deter performance of the finished inks and coatings. These methods also, while achieving the desired outcome in terms of non-skid, low MVTR, often cause a reduction in gloss. Special equipment and techniques generally are required to incorporate the wax and consistency of the wax particle size and stability, without wax separation from the system or coagulation of latex particles, is very difficult to achieve.
The following patents and literature describe the utilization of waxes in formulating inks and coatings and methods of incorporation:
An article by Thankachan, "Incorporation of Wax and Inks and Coating: A Necessity and a Dilemma," American Ink Maker, pages 34-96 (October 1985), discloses the role of a variety of waxes in formulating coatings and inks. Typically, the waxes are incorporated into liquid inks and coatings, as a predispersed medium or stirred and milled into the ink or coating system.
Michelman, et al., "Wax Emulsions and Aqueous Polymeric Coating: Contributions and Mechanisms," Tappi Journal, pages 159-163 (April 1989), discloses the preparation of wax emulsions for use in aqueous polymeric coatings. The mix of emulsion and coating results in a substrate having a lower coefficient and friction, improved rub resistance, barrier properties, better release, better machinability, and the like. The article discusses various concentrations and types of wax and their effect on surface properties of the resultant coating.
U.S. Pat. Nos. 4,942,193; 5,081,174 and 5,229,450 disclose protective compositions based upon base-neutralized acid-functional copolymers incorporating a wax lubricant. The acid-functional copolymers are prepared by solution polymerizing ethylenically unsaturated monomers, e.g., acrylates, styrene and an acid-functional monomer, e.g., acrylic or methacrylic acid. The base-neutralized acid-functional polymer and wax lubricant is dispersed into water thereby forming an emulsion. Optionally, an additive to enhance removability of the coating from a surface is incorporated into the emulsion.
U.S. Pat. No. 3,884,857 discloses the production of ethylene/vinylester copolymers via solvent polymerization wherein molten petroleum, polyethylene and Fischer-Tropsch waxes are added to the polymerization medium.